The theory was/is that given the sheer volume of letter mail it is simply not possible/viable to screen using more intensive measures such as scanners etc. If customs started to manually inspect each item they would need to employ several thousand more staff to start groping everything. Normally what happens is international mail is given one or more types on inspection which includes: 1) canine 2) visual/manual 3) x-ray The theory regarding letter mail appears to have been tested somewhat recently though with an increase in the number of no shows across the board so assuming those letters were prepared in a clean environment using non permeable packaging then they would have had to have been subjected to visual/manual and/or x-ray screening to have been seized. I have heard that they have the ability to x-ray entire boxes of letter mail, something they do when conducting larger operations but it is not inconceivable that they would have started to employ this measure on a more regular basis thus resulting in an increase in small quantity seizures. At the end of the day a lot of what we post and discuss here is pure subjective speculation, we really need a man on the inside working for the boarder protection services to start posting in here, anyone fancy a career change?